1. Field of the Invention
The clinical diagnostic field has seen a broad expansion in recent years, both as to the variety of materials which may be readily and accurately determined, as well as the methods for the determination. One broad category of techniques involves the use of an organic receptor which is able to specifically bind to a particular spatial and polar organization of another molecule. For the most part, these compounds are antibodies, which are able to distinguish between the compound or composition of interest, and other compounds of analogous structure. By virtue of the binding of the receptor to a labeled ligand, one is able to distinguish between labeled ligand which is bound to receptor and unbound labeled ligand.
The observed effect of binding by the receptor will depend upon the label. In some instances, the binding of the antibody merely provides for a differentiation in molecular weight between bound and unbound labeled ligand. In other instances, the presence of the receptor may affect the nature of the signal obtained from the label, so that the signal varies with the amount of receptor bound to labeled ligand. A further variation is that the receptor is labeled and the ligand unlabeled. Where receptors are labeled with two different labels which interact when in close proximity, the amount of ligand present affects the degree to which the labels on the receptor may interact.
In developing an assay, there are many considerations. One consideration is the signal response to changes in the concentration of analyte. A second consideration is the ease with which the protocol for the assay may be carried out. A third consideration is the variation in interference from sample to sample. Ease of preparation and purification of reagents, availability of equipment, ease of automation, and interaction with ligands, are additional considerations, which do not exhaust the various concerns in developing a useful assay.
There is therefore a continuing need for new and accurate techniques which can be adapted for a wide spectrum of different ligands or be used in specific cases where other methods may not be readily adaptable.
2. Brief Description of the Prior Art
U.S. Pat. No. 3,709,868 is exemplary of a radioimmunoassay. U.S. Pat. No. 3,960,834 is exemplary of a spin immunoassay. U.S. Pat. No. 3,654,090 and German Auslegungsschrift No. 2,223,385 are exemplary of enzyme immunoassays. Articles of interest include an article by Ludwig Brand and James R. Gohlke, Annual Review of Biochemistry, 41, 843-868 (1972) and Stryer, Science, 162, 526 (1968). Smith, FEBS Letters 77, 25, (1977) describes a fluorescent immunoassay, where thyroxine is bound to a fluorescer and quenches the fluorescer, the quenching being reversed by binding of antibody to thyroxine. See also, Ullman et al, J. Biol. Chem. 251, 4172 (1976).
An excellent review of chemiluminescence may be found in McCapra, Quarterly Reviews 20, 485 (1966).